Robert Cortez, left, and Roger Aguilar of Bexar County vector control prepare equipment for spraying to eradicate mosquitos at the Southton Service Center on Wednesday, Aug. 22, 2012. The county recently recorded its first West Nile virus death.

Photo By Billy Calzada/San Antonio Express-News

Roger Aguilar of Bexar County vector control tests fogging equipment before driving into the field to eradicate mosquitos at the Southton Service Center on Wednesday, Aug. 22, 2012. The county recently recorded its first West Nile virus death.

Photo By Billy Calzada/San Antonio Express-News

A nozzle on a truck sprays a fog to eradicate mosquitos along Hickory Way in South Bexar County on Aug. 22, 2012. The county recently recorded its first West Nile virus death.

Photo By Billy Calzada/San Antonio Express-News

A Bexar County vector control truck fogs the area near the intersection of Mesquite Bend and Mesquite Cove on Wednesday, Aug. 22, 2012. The county recently recorded its first West Nile virus death.

Photo By Billy Calzada/San Antonio Express-News

Daniel Hinojosa, left, and Jose Segura walk along Hickory Way in South Bexar County as a vector control truck drives by, fogging the area in an effort to eradicate mosquitos on Wednesday, Aug. 22, 2012. The county recently recorded its first West Nile virus death.

West Nile Virus is a potentially serious illness that experts believe is a seasonal epidemic that flares up in the summer and continues into fall. The virus primarily is spread through infected mosquitoes that feed on infected birds then bite humans or animals.

In a small number of cases, the virus has been spread through blood transfusions and organ transplants.

The best prevention is preventing mosquito bites.

The CDC recommends:

• Use insect repellent with an EPA-registered active ingredient when outdoors.

• Wear long sleeves and pants or stay indoors during dusk and dawn when mosquitoes are most active.

There is no specific treatment. Severe cases may require hospitalization so they can receive intravenous fluids, help with breathing and nursing care.

Source: U.S. Centers for Disease Control, City of San Antonio Metropolitan Health District. Compiled by News Researcher Michael Knoop.

Another person in Bexar County has been infected with West Nile virus, city health officials said Thursday, raising the local total to 10.

The most recent victim is an 81-year-old man, said Metro Health spokeswoman Carol Schliesinger, who added that health officials received confirmation of the diagnosis Wednesday.

So far this year, two people have died in Bexar from the disease.

According to Metro Health, the man reported first feeling ill Aug. 12 with symptoms that define the disease, including high fever, loss of appetite, chills and pain in his bones and joints.

He told doctors he hadn't traveled significantly, but that he usually spent two hours a day outside and didn't use mosquito repellent.

Only two of the 10 infected people are younger than 60. Health officials have warned that the elderly and individuals with weakened immune systems are more vulnerable to the disease.

Bexar County's reported incidence rate is small compared with the rest of the state, with the most concentrated outbreak in North Texas over the past few months.

According to data on the Texas State Health Services website, which was updated Thursday, about half the state's 1,066 West Nile cases have been found in Dallas, Tarrant, Collin and Denton counties. And across the state, at least 44 people have died from the disease.

Officials say the numbers are expected to increase through mid-October. There are indications August marked the peak, especially in North Texas. Since symptoms can take two weeks to appear, reporting lags behind when people became infected.

Texas has been working with the CDC this summer to help eliminate mosquitoes that carry the disease, including aerial spraying of insecticide in parts of North Texas. Texas Department of State Health Services Commissioner Dr. David Lakey said that in areas that have received two consecutive aerial sprays, the number of mosquitoes decreased by 93 percent.

While experts say high temperatures may have contributed to the boom in cases, officials are studying what exactly has made it such a deadly year for West Nile, especially in the Dallas area.

“Transmission is contingent on mosquitoes,” Lakey said. “The more you have, the greater likelihood of an outbreak.”

Schliesinger said local health officials advise people to stay indoors during dawn and dusk when mosquitoes are most prevalent. She added that people who venture outdoors during those times should consider wearing mosquito repellent.

Officials also asked residents to check their property to make sure there aren't places where water can sit and become a breeding ground for mosquitoes.